Unable to install QuickTime Pro

You must have upgraded your OS to Snow Leopard, or Lion, to not have a QuickTime System Preference pane.

If that's the case then you have QuickTime Player version 7.6.6 and the registration info is found under the Player menu.

In Snow Leoprad and Lion Quicktime Player is moved to the Utilities folder. Check there first.

Bought QuickTime Pro version 7.2 a few years ago.

Now, I am unable to install it.

QuickTime does not show up in System Preferences Panel and cannot enter serial # info

Current Leopard, Snow Leopard, and Lion operating systems have do away with the older method of alternative Pro Key entry via the "System Preferences Panel" and all now rely on the primary access point within the QT Player 7 application itself under the "About" menu. Registration for all Mac version is now essentially as described HERE with that exception that you must download and install the appropriate version of QT 7 that is compatible with your Leopard or Snow Leopard/Lion OS.